Injection molded parts with small dimensional tolerances are in high demand in various industries (e.g., electronic, automotive, etc.). In these applications, the thermoplastic composition must have good flow properties so that it can quickly and uniformly fill the small spaces of the mold cavity. In addition, the formed part should exhibit desired qualities such as flexibility while withstanding expected stresses during use.
Injection molded polymer blends that exhibit flexibility in addition to high strength and resistance properties are of significant commercial interest. Such blends have been formed in the past by uniformly mixing an elastic component with a thermoplastic polyolefin such that the elastomer is intimately and uniformly dispersed as a discrete or co-continuous phase within a continuous phase of the polyolefin. Vulcanization of the composite crosslinks the components and provides improved temperature and chemical resistance to the composition. When vulcanization is carried out during combination of the various polymeric components it is termed dynamic vulcanization. Unfortunately, injection molded products of small dimensions formed from dynamically vulcanized polyolefin blends fail to provide the desired strength and resistance properties in many applications.
Polyarylene sulfides are high-performance polymers that may withstand high thermal, chemical, and mechanical stresses and are beneficially utilized in a wide variety of applications. Polyarylene sulfides have often been blended with other polymers to improve characteristics of the product composition. For example, elastomeric impact modifiers have been found beneficial for improvement of the physical properties of a thermoplastic composition. Compositions including blends of polyarylene sulfides with impact modifying polymers have been considered for high performance, high temperature applications.
Unfortunately, elastomeric polymers generally considered useful for impact modification are not compatible with polyarylene sulfides and phase separation has been a problem in forming compositions of the two. This can be particularly problematic when forming products having small dimensions. Attempts have been made to improve the composition formation, for instance through the utilization of compatibilizers. However, even upon such modifications, compositions including polyarylene sulfides in combination with impact modifying polymers still fail to provide product performance as desired, particularly in small dimension injection molded parts that require both high heat resistance and high impact resistance.
What are needed in the art are thermoplastic compositions that can be injection molded to form small dimension products that exhibit high strength characteristics as well as resistance to degradation, even in extreme temperature environments.